1. Field of the Invention
The present invention relates to the optical projection of television images and, more particularly, to television projection systems of the type characterized by a plurality of color separation assemblages (typically red, green and blue), each incorporating cathode ray and projection optics components, certain of which are enclosed within a cathode ray tube. These color separation assemblages register enlarged color separation images on a viewing screen for visual fusion by observers.
2. The Prior Art
Various systems have been proposed for projecting and enlarging video images.
In one such system, the real image generated in a television tube with a conventional, three color shadow mask is imaged by a single optical assemblage. It is known that the information bearing area of a conventional cathode ray tube is reduced by more than 50% of its theoretical maximum in the presence of a three color shadow mask. The shadow mask effectively serves to isolate the color separation dots that are needed in a single television tube to produce a multicolor image but undesirably introduces shadowed interstices that contribute no information. The resulting composite image is characterized by unduly low resolution and contrast.
In another such system, three distinct color separation assemblages generate and project red, green and blue color separation images for registration on the viewing screen. Each color separation assemblage includes, in axial alignment: a forwardly directed electron gun; a rearwardly directed phosphor target; a forwardly directed centrally apertured positive mirror that is positioned between the gun and the target; and a correcting lens that is positioned forwardly of the target. The gun, mirror and target are mounted within a cathode ray tube. The correcting lens is positioned outside the cathode ray tube. The mirror and correcting lens constitute a Schmidt optical system. Here image degradation has been caused by optical mounts that are unduly difficult to adjust precisely and that unduly block portions of the catadioptric field, optical surface configurations that do not cooperate optimally, and phosphor target constructions having energization response characteristics that unduly vary in time.